1. Field of the Invention
The present invention relates to a housing for holding a slab geometry laser gain media, and specifically a housing which allows for close-coupling of one or two laser diode pump arrays.
2. Discussion of Prior Art
When the slab laser geometry was first being developed in the early 1970's, laser diodes as an efficient pump source were not available. It is only recently that both the technology and availability of laser diode bars, and a method for packaging them, has made two dimensional laser diode pump arrays a commercial reality. A technique for producing such a two dimensional diode laser array is demonstrated in the U.S. Pat. Nos. 5,040,187 and 5,128,951 to Karpinski (1991 and 1992). The advent of lower cost laser diodes for efficient pumping has led to the need for a slab housing which allows for the efficient coupling of a two dimensional diode array into a slab type gain media.
A difficulty with a laser diode array pump source is the rapid divergence of the diode laser light in one axis. One solution to this problem is to place the surface of the diode laser pump array as close as possible to the surface of the gain media. This type of pumping geometry is called close-coupled. An additional constraint on using a diode array for the pump source is that the diode array surface can not be exposed to a liquid coolant which must flow over the gain media when operating above medium average powers. Thus, a means of holding the slab is needed which is specifically adapted for close-coupling a two dimensional diode pump array, and yet isolating the array surface from the coolant.
In U.S. Pat. Nos. 4,378,601 to Eggleston III et al. (1983), 4,653,061 to Fukae (1987), 4,468,774 to Robbins (1984), and 4,993,041 to Sidler et al. (1991), there is described a slab laser housing where the slab is mounted to the head body via some style of side bars or rails. These side bars can serve a variety of functions, such as: thermal insulation of the side faces of the slab, mechanical isolation from thermal expansion of the housing, distribution of the coolant via a series of holes, and making the slab removable for inspection and cleaning. But the side bars are unnecessary if the housing is designed specifically to provide the functions of: thermal insulation, mechanical isolation, coolant distribution, and provides for easy access to the slab optical surfaces.
Another disadvantage of these earlier patents is that they do not provide a housing which allows for placing the pump source close to the gain media while simultaneously isolating the pump source surface from the coolant. These patents all depict a lamp style pump source. With a lamp pump source, one often uses a coolant flooded reflective cavity to direct the pump light into the gain media. This arrangement allows for a more efficient and spatially uniform pumping of the gain media. But this reflective pump cavity is unnecessary if the pump source is a two dimensional laser diode array.
The U.S. Pat. No. 4,984,246 to Cabaret et al. (1991) shows one approach for coupling a diode array pump source to a slab gain media. This patent shows a light duct formed by a set of reflective walls for conveying the pump light to the slab gain media. The diode pump array is not the same size as the slab it is pumping. The purpose of the light duct is to make the pump light spatially uniform over the slab gain media. One disadvantage of this approach are the losses at the reflective surfaces of the light duct.